1. Field of the Invention
This invention relates to compositions for removing or stripping paint, varnish, and like coatings from wood and metal surfaces.
2. Review of the Prior Art
Removal of protective coatings from wood and metal surfaces has long been a difficult and laborious operation involving the use of flame, heat, and/or chipping tools. Such labor has been minimized by using solvents to soften and/or lift a coating from a protected surface. Compositions for removing protective coatings have generally utilized methylene chloride and other halogenated aliphatic hydrocarbons.
Paint and varnish removers are of two main types according to method of use: application removers and immersion removers. Application removers are usually applied by brushing or spraying and are used for small jobs or for items that cannot be immersed. Immersion removers are used as either cold or hot baths where it is practical and cost efficient to install equipment that can strip numerous items. Cold baths contain solvents such as methylene chloride, and hot paths often contain caustic soda.
As disclosed in U.S. Pat. No. 2,495,729, aliphatic alcohols or cyclic aliphatic oxides, such as tetramethylene oxide, are mixed with an aliphatic acid ester, such as ethyl acetate in acetone, and a surface active agent, such as a long chain alkylbenzene sulfonate, and are effective for vertical surfaces because a film-forming base material, such as wax, cellulose nitrate, and cellulose acetate, is added to increase the viscosity and form a protective film which enables the solvent and softening agents to be confined within the film to exert maximum softening and solvent action. The composition includes methylene chloride as the preferred sole active organic solvent plus a second component such as benzene, methanol, and acetone to form preferred binary mixtures.
U.S. Pat. No. 3,179,609 describes compositions useful for removing coatings and finishes such as paints, varnishes, lacquers, shellac, gums, and natural and synthetic resins.
U.S. Pat. No. 3,538,007 discloses a paint stripper comprising 54-77 parts of chlorinated liquid hydrocarbon solvent, 1-4 parts of carboxylic acid having 1-4 carbons, 1-6 parts of propargyl alcohol, 0-2 parts of non-ionic wetting agent, 0-15 parts of liquid aromatic hydrocarbon solvents, 0-6 parts of a coupling agent, 0-30 parts of phenol or alkyl substituted phenol, 0-2 parts of a thickener, and 0-2 parts of an evaporation retarder. The aromatic liquid hydrocarbon can be benzene, toluene, or xylene.
U.S. Pat. No. 3,574,123 describes a paint stripper comprising 50-90 parts of a chlorinated liquid hydrocarbon solvent, 2-15 parts of a lower aliphatic alcohol or glycol ethers, 0.1-15 parts of a lower carboxylic acid, 2-30 parts of hydroxybenzenes, 2-10 parts of a fatty acids sulfonate or a salt of a fatty amine carboxylic acid, and 0.1-10 parts of aqueous ammonium bifluoride. This composition can also contain inert organic aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, otho-ethyltoluene, di-ethylbenzene, and isopropyl benzene, the lower alkyl substituted benzenes boiling at 170.degree. F. and higher being preferred.
U.S. Pat. No. 3,592,691 describes the removal of photo resist mask residuals from a semiconductor substrate by immersing the substrate in a photoresist solvent and heating the solvent at 150.degree.-250.degree. C. and at a pressure of about 300 psig for a time period of 1/4-3 hours. The solvent composition comprises trichloroethylene, isopropanol, and xylene with up to a few percent of methylene chloride. The isopropanol may be replaced wholly or partially with lower boiling point aliphatic alcohols such as ethanol.
U.S. Pat. No. 3,743,542 describes a method for removing paint from metal surfaces by boiling a solvent or solvent mixture and contacting the painted metal surface with the vapors of the solvent mixture, preferably while refluxing the vapors in a closed system. It is especially useful for removing durable paints such as those based on vinyl, acrylic, or epoxy resins. The stripping composition comprises hydrogenated aromatic solvents and aliphatic alcohols.
U.S. Pat. No. Re 27,432 is directed to a process for removing polymeric materials from processing equipment. It teaches numerous solvents known for dissolving vinyl halides such as trimethylene oxide, tetramethyl urea, dimethyl acetamide, tetrahydrofuran, cyclohexanone, cyclopentanone, cyclohexene oxide, diethyl acetamide, methyl ethyl ketone, and dioxane. It also teaches that these solvents vary in dissolution strength with the molecular weight of the compound to be dissolved and that tetrahydrofuran successfully removes both homopolymer and co-polymer contaminants having low or high molecular weights.
U.S. Pat. No. 3,784,477 relates to removal of paints, varnishes, and similar finishes from wood and metal objects without damage to grain or glue joints. It teaches that xylene or aromatic naphthas can be used as an extender for dimethylformamide or dimethyl acetamide, with little change in paint removal activity, and further that xylene can be diluted or extended freely with methyl alcohol up to about 20% of its weight.
U.S. Pat. No. 4,595,396 teaches the solubility of trioxane in methanol, absolute ethanol, and 95% ethanol at temperatures below and above ambient. Such solutions are used for fuel transport and as fuel.
Trioxane-containing lacquer removers for alkyd resins are disclosed in German Offenlegungsschrift No. 2,118,870. They consist of 4-7:1-3 parts diol acetols, such as 1,3-dioxolane, and trioxane for retention of the volatile acetals. They optionally contain ethyl cellulose.
Solutions comprising trioxanes and ethyl acetate for removing alkyd resin coatings are also described in German Offenlegungsschrift No. 2,123,563. They optionally contain ethyl cellulose as a retention agent. An alkyd resin coating treated with a 4:1 mixture of ethyl acetate: trioxane was removable within 0.5 minute after application and hardened (due to solvent evaporation) after 120 minutes, as compared to 0.5 and 50 minutes, respectively, for pure ethyl acetate.
Substantially all currently used strippers contain chlorinated hydrocarbons and particularly methylene chloride which is a potentially harmful solvent. There is accordingly a need for a solvent having fast lifting speed for common coatings which is also harmless to the user.
Accordingly to the "Kirk-Othmer Encyclopedia of Chemical Technology," Vol. 16, p. 763, a typical Methylene Chloride Remover contains 70-85% methylene chloride, 5-10% alcohol, and 0-10% hydrocarbon solvent or ketones, the remainder being paraffin wax, methylcellulose, an amine, and surfactants or emulsifiers.
Because immersion stripping has many practical advantages, there is also a need for a stripper composition for use in hot baths that is less volatile than one based on methylene chloride (b.p.=42.degree. C.), less toxic, and less painful upon skin contact.